The present invention relates to a telescopic extension for an intake conduit of a vacuum cleaner, comprising an internal tube and an external tube sliding one inside the other, so that the length of the same extension can be adjusted telescopically and that the same tubes can be clamped in a relative selected positions to form a handle of desired length.
Generally in vacuum cleaners a suction mouth or a cleaning brush are connected to a vacuum cleaner by means of a conduit comprising a rigid section that facilitates its grasp, and a flexible section.
The rigid conduit section is formed by a telescopic extension comprising an internal tube and an external tube, sealingly sliding one inside the other, so as to convey air and dust in the flexible section and to constitute a handle that can be adjusted in length, suitable for maneuvering the suction mouth or the cleaning brush. Thus the extension should be capable of transmitting longitudinal forces of some magnitude.
The European patent application No. 0293518 describes a telescopic extension for a vacuum cleaner, comprising an internal tube and an external tube, sliding one inside the other, wherein a sleeve of suitable plastic material is mounted inside a flared section of the external tube, so that it fits over the internal tube. The internal tube is provided with a row of notches of a preselected shape, hemispherical or hemicylindrical, appropriately spaced, suitable for receiving a constraining element formed by a sphere or by a small cylindrical bar, supported by the sleeve itself.
In the sleeve there is also a means for manual operation, constituted by a ring nut or by a pushbutton which, normally, under the action of a spring, keeps an element of thrust in engagement with said constraining element and forces it into one of the notches of the internal tube, so as to lock the latter with respect to the external tube. By pressing said means for operation, against the action of the spring, the element of thrust is disengaged from the constraining element, which leaves the internal tube free to slide with respect to the external tube, allowing the length of the same extension to be adjusted.
In this telescopic extension, however, clearances appear in time which hinder the adjustment of its length, because in the element of thrust in plastic material impressions appear due to the fact that the contact with the constraining element made of steel takes place in an area substantially limited to a point or a line, and thus the specific pressure is very high. These impressions, which are formed in a direction substantially normal to the direction of movement of the element of thrust, tend to increase in time.
When the element of thrust is deformed, the constraining element remains loose in the notches of the internal tube, and is no longer capable of firmly locking the latter with respect to the external tube, in the desired position.
Another problems of said known telescopic extension arise from said flared section of the external tube, which needs complex operations for manufacturing.
The U.S. Pat. No. 3,351,363 describes a telescopic extension for vacuum cleaners, comprising an internal tube and an external tube, sealingly sliding one inside the other, wherein a sleeve in plastic material is mounted overhanging on the external wall of the external tube and is fastened to it by deformation of the same external tube inside an annular groove on it, or it is mounted inside a flared section of said external tube and is fastened by upsetting an edge of said external tube to act as a guide of the internal tube. The internal tube is provided with a row of hemispherical notches, appropriately spaced, suitable for receiving a constraining element formed by a ball that can be movably supported radially by the same sleeve.
In the sleeve there is also mounted a sliding or rotating manually-operated ring nut which, normally, under the action of a spring, thrusts said ball radially, through a element of thrust, into one of the notches of the internal tube, so as to lock the latter in the desired position with respect to the external tube. By moving the ring nut, against the action of the spring, the ball is disengaged and leaves the internal tube free to slide with respect to the external tube and allows the length of the extension itself to be adjusted.
One of the main disadvantages of this telescopic extension is represented by the fact that the connection between sleeve and external tube is accomplished by the latter's deformation through expansion instruments and through an upseting instrument. This operation, in addition to making the manufacturing cycle more complex and more expensive, can jeopardize the integrity of the tube, thus increasing the number of rejects.
Another disadvantage of the embodiment of the extension described having said sleeve overhanging, is represented by the fact that the sleeve constitutes a component that is too weak to effectively support the repeated stresses to which it is subjected during the operations for which the extension is destined.
Also in said latter telescopic extension impressions appear in the element of thrust in plastic material due to the fact that the contact with the element of constraining made of steel takes place in a very narrow area substantially limited to a point. Therefore in time clearance appears between the element of thrust and the element of constraining which remains loose in the notches of the internal tube, and is no longer capable of firmly locking the latter with respect to the external tube, in the desired position.
An object of the present invention is to provide a telescopic extension for vacuum cleaners in which the problems connected with the contact between the element of thrust and the constraining element are overcome, so as to to maintain maximum efficiency in time. Another object of the invention is to provide a telescopic extension that should be made and assembled in a manner that is easy and safe, without involving deformations of the external tube.
A further object of the present invention is to provide a telescopic extension that is strong, functional, reliable, and exempt from loose clearances even after prolonged use.